Antimicrobial peptides (AMP) are found in nature and have been isolated from several organisms including animals and plants. In recent years these molecules have shown an important anti-pathogenic capacity over Gram positive, Gram negative and fungi. AMPs are usually composed of 12-50 cationic and amphipathic amino acids (Broekaert et al., 1997; Zasloff de 2002, Marshall and Arenas, 2003). The natural AMP are divided into groups characterized by peptides formed by β sheets, α-helices, extended structures and helix loop or loop structures, and of them, the first two are the most abundant (Dathe et al., 1999; Gao et al., 2000; Lehrer and Ganz, 2002; Bulet et al., 2004). The interaction between AMPs and their target cells is markedly influenced by factors such as the type and scope of their structure, cationic property, hydrophobicity, amphipathic property and amino acid sequence (Yeaman and Yount, 2003; Jenssen et al., 2006; Soltani et al., 2007). Over 2300 peptides have been described and information on their structures, properties and mechanisms of action can be found in databases such as APD, ANTIMIC and AMPer.
In recent times the AMP have grabbed the attention as new substitutes of conventional pesticides and antibiotics, as pathogens do not develop resistance to them because of their mechanism of action (Yeaman and Yount, 2003). However, the use of peptides as alternative drugs has encountered some difficulties, among these we highlight the low recovery obtained after extraction from the tissue of origin. Therefore, obtaining by chemical synthesis or expression the protein in a recombinant microorganism strategy has become necessary for further studies. Interestingly, synthetic analogs or AMP derivatives have been successfully developed on the basis of natural peptides, generating significant improvements in their antimicrobial activity.
Most marine invertebrates are fixed to a substrate. Due to this sedentary condition, these organisms have evolved effective antimicrobials mechanisms among which are the AMPs (Tincu and Taylor, 2004). AMPs have been purified mainly from mollusks like mussels, oysters, scallops and gastropods. Arenas et al. (2009) obtained and characterized a form of an AMP native of chilean oyster (A. purpuratus hemocytes) by means of chemical synthesis. This new molecule (Ap-S) showed the presence of a secondary structure polyproline type, with a reduced amount of β sheet due to differential distribution of hydrophobic and hydrophilic residues in two well defined zones in N- and C-terminus, compared to the native peptide (Ap). Ap-S showed no cytotoxic effect in fish cell line CHSE-214. These findings in the Ap-S molecule newly generated, make their evaluation for various biotechnological applications be a reasonable option, including the exogenous application to control important plant pathogens. In this regard, the scaled up synthesis of this peptide becomes important for possible industrial application.